The aim of this project is to attempt to localize alpha-fetoprotein (AFP) secreting malignant tumors in an experimental model using antibodies labeled with different radiopharmaceuticals in order to determine the optimal reagents for this purpose. This investigator has been growing AFP-producing human tumor lines in nude mice as a model system to study the biodistribution and clearance of radiopharmaceutical labeled antibodies. 1131- labeled monoclonal AFP antibodies have successfully localized the AFP-secreting tumor cells in the mouse model system. They have begun to delineate its plasma clearance and biodistribution. The IgG monoclonal antibody is being compared in this model to (Fab)2 fragments as to their relative effectiveness. Chemical methods for linking indium and technetium to hybridoma immunoglobulin molecules to optimize the retention of their antigen-binding capacity are currently being investigated.